Many metallic vapor laser tubes preferably are maintained at elevated temperatures of the order of 1000.degree. C. for certain types of desired operation. Customarily, such laser tubes are enclosed within an oven to maintain the elevated temperature thus causing the metallic element contained within the sealed enclosure of the laser tube to become vaporized. Electrically conductive electrodes sealed within the laser tube generate an arc therebetween in response to the application of a suitable source of electrical energy to the external terminals of the electrodes. The laser tube, thus energized and maintained at a suitable temperature, develops sufficient vapor pressure of the metallic element causing the metal vapor to be raised to an energy level at which it will emit laser energy output.
In the prior art, metal vapor laser tubes customarily included "hot" zones which were generally disposed between the electrodes that generated the electrical discharge. Moreover, the windows conventionally disposed at either end of the laser tube for transmitting the laser energy were usually maintained at a significantly lower temperature which was generally referred to as the "cold" zone. Though these windows may not actually be operated at what is commonly regarded as a cold temperature, they were nonetheless "cold" relative to the hot zone. As a result, many prior art metallic vapor laser tubes were limited in life and efficiency because of the fact of the metal vapor would migrate to the cold zone on the windows and become deposited upon the windows by a partial condensation, thereby rendering the windows partially opaque to the laser energy emitted so that the laser beam could not be sufficiently transmitted outside the confines of the laser tube.
Additionally, the hot metal in its vaporous form migrated in a continuous particle flow to the cold zone so that eventually there was very little metal remaining in the hot zone where the laser emission takes place. As a result, laser action after some determinative period of time ceased to occur for lack of sufficient vaporized metal in the hot zone resulting in insufficient vapor pressure to support and maintain the desired lasing action.
Many metallic vapor laser tubes of the prior art sought to overcome this problem by introducing an inert buffer gas such as argon, for instance, or helium between the hot zone and the relatively cold zone. As a result, the windows, were desirably isolated from the metallic vapor, thus preventing condensation of the metallic vapor upon the windows and obviating the resultant undesirable diminished efficiency of operation. Although the use of such a buffer gas in prior art metallic vapor laser tubes was an advance and improvement in the art, it still left much to be desired because of several inherent disadvantages which the presence of a buffer gas introduces.
For example, the discharge within the prior art type of tube using buffer gas, was always of a necessity a mixture of buffer gas and the vaporized metal. In certain cases where there was no interchange of energy between the two systems, i.e., the buffer gas and metallic vapor, the buffer gas would absorb considerable energy from the power supply. On the other hand, when there is an energy transfer between the two gas systems which is not essential for pumping energy into the metallic vapor, it is possible that such interaction with the buffer gas can inhibit the desired stimulated emission.
Moreover, even with the advantages which the use of a buffer gas provides in diminishing condensation of the metallic vapor on the cold windows, eventually all the metal may be transposed from the hot zone to the relatively cold zones which are presented by the walls of the laser tube, for example, outside the hot zone. Consequently, after some determinable period of operation the laser tube must be replenished with an additional amount of metal to provide the basis for generating the metallic vapor for the desired stimulated emission in the hot zone.
Accordingly, there is an existing need for an improved metal vapor laser tube which will operate at an elevated temperature without having the so-called "hot" and "cold" zones conventionally relied upon in the prior art.